RACIAL, TYPES KEITH. 453 
the muscles, the heart, the hmgs, the organs of digestion, particularly 
the jaws; hence the marked changes in the face for the form of the 
face is determined by the development of the upper and lower jaws. 
The rational interpretation of acromegaly is that it is a pathological 
diorder of the mechanism of adaptational response; in the healthy 
body the pituitary is throwing into the circulation just a sufficiency 
of a growth- regulating substance to sensitize muscles, bones, and other 
structures to give a normal response to the burden thrown on the 
body. But in acromegaly the body is so flooded with this substance 
that its tissues become hypersensitive and respond by overgrowth to 
efforts and movements of the slightest degree. It is not too much to 
expect, when we see how the body and features become transformed 
rtt the onset of acromegaly, that a fuller knowledge of these growth 
mechanisms will give us a clue to the principles of race differentiation. 
There must be many other mechanisms regulated hj hormones with 
wdiich we are as yet totally unacquainted. I will cite only one in- 
stance — that concerned in regulating the temperature of the body. 
We knoAV that the thyroid and also the suprarenal glands are con- 
cerned in this mechanism; they have also to do with the deposition 
and absorption of pigment in the skin, which must be part of the 
heat-regulating mechanism. It is along such a path of inquiry that 
we expect to discover a clue to the question of race color. 
This is not the first occasion on which the doctrine of hormones 
has been applied to biological problems at the British Association. 
In his presidential address to the zoological section, at Sheffield, in 
1910, Prof. G. C. Bourne applied the theory to the problems of evolu- 
tion; its bearing was examined in more detail in an address to the 
same section by Prof. Arthur Dendy during the meeting at Ports- 
mouth in 1911. At the meeting of the association, at Newcastle, in 
1916, Prof. MacBride devoted part of his address to the morpho- 
genetic bearings of hormones. Very soon after Starling formulated 
the hormone theory, Dr. J. T. Cunningham applied it to explain the 
phenomena of heredity (Proc. Zool. Soc, London, p. 434, 1908). 
Nay, rightly conceived, Darwin's theory of pan-genesis is very much 
of the same character as the modern theory of hormones. 
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